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Lactose Intolerance


Lactose intolerance is also called milk intolerance, dairy product intolerance, lactose malabsorption, or milk sugar intolerance. Lactose is a sugar molecule made up of glucose and galactose. It is present in milk and milk-containing products. When the small intestine is deficient in a digestive enzyme named lactase, then the condition arises, referred to as lactose intolerance. If lactase enzyme is not sufficient, then lactose is not broken into simpler sugars, glucose, and galactose, which leaves lactose undigested and causes multiple digestive issues. At the moment, 75% of the world’s population is suffering from lactose intolerance. Lactase deficiency usually develops before the age of 20. The signs and symptoms of lactose malabsorption depend on the amount of lactase produced or the amount of lactose consumed. Some people may be able to digest lactose to some extent, whereas others may have complete intolerance. Lactose intolerance differs from milk allergy, which can result in anaphylaxis.

Types And Causes

There are three types of lactose intolerance.

1. Primary lactose intolerance:

This type of lactose intolerance is very common. In this type, lactase production is naturally reduced with age. This is the result of the normal aging process in the body. This reduction is due to diverse diets and less consumption of milk with age which intuitively reduce lactase production.

2. Secondary lactose intolerance:

This is due to underlying disorders like.

 This malabsorption can be reversed by treating the underlying condition.

3. Developmental or congenital lactose intolerance. 

This is due to the hereditary factors following the autosomal recessive patterns. The child adopts this trait when he gets the same intolerant Gene variant from both mother and father. Premature infants can also develop lactose intolerance as lactase is produced in sufficient amount in 3rd trimester.

Congenital lactase deficiency is also known as congenital alactasia. It is a rare disorder. In this disorder, infants cannot break up lactose from mothers' milk or formula milk. This results in severe diarrhea, becoming the leading cause of severe dehydration and weight loss in infants. This can be fatal if not caught abruptly.

Risk Factors

Following factors can increase your chance of having lactose intolerance;

  • Premature birth(Lactase-producing cells in the small intestine are formed in the 3rd trimester).
  • Aging (Adulthood).
  • Complications of chemotherapy.
  • Ethnicity.
  • Small intestine bacterial overgrowth.
  • Celiac disease.
  • Crohn’s Disease.
  • Radiotherapy of the stomach.
  • Intestinal infections.
  • Ulcerative colitis.


Lactose intolerance is found in 48% of people in the USA, being higher in African Americans.  Primary lactose intolerance is common in certain ethnicities like Hispanic, Asian, African, and American. It occurs 5% in North Europeans. Congenital lactase deficiency is most common in Finland. Lactose intolerance is very common in West African, Arab, Greek, Jewish, and Italian. Prevalence is very low in people who use unfermented milk products for long periods. 

Signs And Symptoms

Following signs and symptoms may begin within 30 minutes to two hours after eating lactose-containing food or dairy. The severity of symptoms relies on the amount of lactose consumed.

  • Flatulence (gas,farting)
  • Bloating
  • Abdominal cramps.
  • Nausea.
  • Vomiting
  • Diarrhea
  • Constipation
  • Tummy pain


Lactose tolerance tests are performed if persistent symptoms occur after drinking or eating dairy products. Some preparation is required before the test. It includes fasting for 8 to 12 hours, no smoking or exercise a day before the test, and discontinuing the use of antibiotics for two to four weeks before the Test. The two types of tests to check lactose tolerance are:

1. Glucose blood test (lactose intolerance test):

In this test, a liquid containing lactose is asked to drink, and after two hours, a blood sugar level is checked. If there is no rise or slight rise in blood sugar level, it shows the body is not properly absorbing or digesting lactose.

2. Hydrogen breath test:

In this test, a liquid containing high lactose is asked to be drunk, and the amount of hydrogen in each breath before and after the drink is calculated. An excessive amount of hydrogen excretion in each breath indicates Lactose malabsorption.

3. Stool acidity test:

It is done in babies and children in which the other two tests cannot be performed. In this test, the stool is tested for lactic acid produced by malabsorbed lactose in the colon.

Differential Diagnosis

Some disorders resembling lactose intolerance may include;

  • Irritable bowel syndrome
  • Milk protein intolerance.
  • Milk allergy (immune reaction)
  • Sucrase deficiency
  • Diabetic diarrhea
  • Celiac disease


There is no particular treatment or cure for lactose intolerance. But with certain lifestyle modifications, it can be managed. Treatment includes: Correction of any underlying condition interfering with the absorption of dairy products.

Following a low lactose diet.

  • Consuming small portions of dairy to improve tolerance to dairy. Milk should be consumed with food. It decreases digestive time and improves absorption without any symptoms.
  • Adding lactase supplement in the form of powder liquid or drops In the diet. Some effective lactase enzyme supplements are Lactaid, lactrase, lactase, dairy ease, and lactrol.
  • Food containing a high amount of lactose should be strictly avoided. It includes Milk, evaporated milk, condensed milk, buttermilk, milk powder, ice cream, yogurt, whey, cottage cheese.
  • Probiotics containing active or live cultures help keep the digestive system active and healthy.


The outcome of lactose intolerance is good with dietary restrictions. It is not a lethal disorder; however, the absence of dairy products can result in some proteins and vitamin deficiencies like calcium deficiency can lead to osteoporosis, malnutrition, osteopenia, etc.  

Lifestyle Modifications

There is no way to naturally increase the body’s lactase production, but certain lifestyle changes greatly affect symptoms associated with lactose intolerance. It includes:

  • Using lactose-free milk, yogurt, and cheese.
  • Using calcium-fortified milk like coconut milk, rice milk, almond milk, or soy to overcome the deficiency that is acquired by reducing the use of dairy
  • Do not cut off dairy completely from the diet. Instead, add small servings.
  • Reintroduce lactose after some time as it encourages the growth of bacteria that help in lactose absorption.
  • Add lactase enzyme in the form of powder or liquid to make lactose digestible.
  • Eggs, beef liver, and yogurt consumption will help maintain vitamin D.
  • Green leafy vegetables salmon, sardines, fortified cereals, juices, oranges, almonds, tofu, Brazil nuts, kale, and dried nuts are good sources of non-dairy calcium.
  • Hard cheese like swiss or cheddar has very little quantity of lactose, so it can be consumed as an alternative to the other cheese.

Our clinical experts continually monitor the health and medical content posted on CURA4U, and we update our blogs and articles when new information becomes available. Last reviewed by Dr.Saad Zia on May 23, 2023.



Lactose Intolerance - NIDDK (nih.gov)


Lactose intolerance: An update on its pathogenesis, diagnosis, and treatment - ScienceDirect